U.S. Pat. No. 4,983,107 (hereinafter called "prior art") to Steffens et al. disclosed a multistage rotary piston vacuum pump including a cooling system provided to reduce too intensive heating and thus expansion of the rotary pistons (4, 5) having two shafts (2, 3) extended downwardly with blind bores (73, 74) longitudinally formed in the two shafts (2, 3) and coolant flowing through the bores (73, 74) for cooling the shafts; and each rotor (4-9) being made of claw type having a ceramic claw (66) secured to an ironic central body (65) by screw (67) for radiating heat for less radial expansion.
However, the rotary pump of Steffens et al. still has the following drawbacks:
1. The shafts (2, 3) should be vertically erected in order to gravitationally return the coolant after absorbing the heat, thereby limiting the installation choices and influencing the piping arrangement of the whole fluid delivery system.
2. The coolant does not enter the internal portion of the pistons (4, 5) and only flows through the bores (73, 74) for merely dissipating heat of the central portion of the pistons (4, 5) near the shafts (2, 3), unable for efficiently removing heat from the pistons.
3. The ceramic claw (66) as fixed on the central body (65) of the rotor may be easily loosened or separated to damage the pump.
The present inventor has found the drawbacks of the conventional rotary vacuum pump, and invented the present rotary compression equipment as internally cooled.